Silas H.L. Wu wrote two excellent books back in the 1970s, published by Harvard University Press, on two topics not duplicated in any books since then.
His 1970 book, Evolution of the Palace Memorial System 1693 – 1735, examines how Emperor Kangxi and Yongzheng kept abreast of what was happening in the vast Chinese empire.
His 1979 book is a biography of Emperor Yongzheng.
To the uninitiated, he is an unimpressive Emperor compared to his father, Kangxi, and his son, Qianlong.
But the truth is that during his short reign of 12 years and 7 months, he was a hard-working Emperor.
He refined the memorial system of communication that allowed him to have secret communications with far-flung court officials.
The book Passage to Power: Kang Hsi and his Heir Apparent by Silas HL Wu, published by Harvard in 1979, narrates the dilemma faced by Kang Hsi throughout his long 61-year reign to select a worthy heir out of 36 sons from 40 consorts.
His first choice, which is his oldest son, Yin Jeng, was anointed as heir, discarded, and reanointed again, only to be ultimately discarded in favour of the 4th son, Yin Zhen (era name Yongzheng).
Coincidentally, Yongzheng was also succeeded by his 4th son, Qianlong.
Passage to Power narrates the subsequent struggles between Emperor Yongzheng and his siblings for control of the throne.
These books make for fascinating reading. Highly recommended.
